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Old 07-04-2018, 09:25 AM   #1876
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Is there a way to verify how intense are the winds generated by Orbiter? The AFDS on final approach is unable to keep track of the lateral path due to the winds, it chases the diamond right and left all the way down to the RWY in a series of S-turns. That's not a very stable approach. Not even Eastwood in "Space Cowboys" had done such a scary thing
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Old 07-04-2018, 09:58 AM   #1877
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Quote:
Originally Posted by Wolf View Post
 Is there a way to verify how intense are the winds generated by Orbiter? The AFDS on final approach is unable to keep track of the lateral path due to the winds, it chases the diamond right and left all the way down to the RWY in a series of S-turns. That's not a very stable approach. Not even Eastwood in "Space Cowboys" had done such a scary thing
They seem to be quite high at times... in the landing scenario I'm using I think I'm getting crosswinds around the 15 knot limit.
There are some issues with lateral control in the current code in the trunk. I've changed some things in the OrbitersimBeta branch, both in the FCS and in the Orbiter aerosurface functions used, and now it isn't that dramatic at all... but the rudder doesn't seem to do much (and the yaw FCS channel isn't responding as expected to rolls )

Anyway, I thought of making one of those "wind socks", but it wouldn't be of much use to have it in the ground while you're flying at 30kft...
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Old 07-04-2018, 12:33 PM   #1878
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Quote:
Originally Posted by GLS View Post
 They seem to be quite high at times... in the landing scenario I'm using I think I'm getting crosswinds around the 15 knot limit.
There are some issues with lateral control in the current code in the trunk. I've changed some things in the OrbitersimBeta branch, both in the FCS and in the Orbiter aerosurface functions used, and now it isn't that dramatic at all... but the rudder doesn't seem to do much (and the yaw FCS channel isn't responding as expected to rolls )

Anyway, I thought of making one of those "wind socks", but it wouldn't be of much use to have it in the ground while you're flying at 30kft...
Where the 15kts crosswind assessment comes from? Is there a way to find the actual winds in sim? What is the logic behind this feature, wind direction and intensity are generated randomly? And what about the change as a function of altitude? (Intensity rising as altitude increases plus change of direction with altitude due to Coriolis effect)? What about terrain also? Does it interfere and alter winds or orography is just ignored?

Sorry I did not mean to flood you with all these questions (out of topic BTW) but I was wondering that maybe you know the logic behind Orbiter winds and how it works

Last edited by Wolf; 07-04-2018 at 03:14 PM.
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Old 07-04-2018, 04:05 PM   #1879
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Quote:
Originally Posted by Wolf View Post
 Where the 15kts crosswind assessment comes from?
I did some math.

Quote:
Originally Posted by Wolf View Post
 Is there a way to find the actual winds in sim?
More math?

Quote:
Originally Posted by Wolf View Post
 What is the logic behind this feature, wind direction and intensity are generated randomly? And what about the change as a function of altitude? (Intensity rising as altitude increases plus change of direction with altitude due to Coriolis effect)? What about terrain also? Does it interfere and alter winds or orography is just ignored?
Probably there is a pattern, as I get pretty much the same wind speed and direction every time I run a certain scenario... I don't know if Martin posted info about the winds, but you can always ask.
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Old 07-05-2018, 09:14 PM   #1880
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In relation to the question here, from diagram 10.2 in JSC-11174:
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Old 07-05-2018, 10:54 PM   #1881
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Thanks for finding that schematic GLS. I'm currently in process of redoing the SRB meshes and I needed to be sure of the locations of the holddown posts. This is what I got so far: https://www.dropbox.com/s/j8rh2zpdsu..._aft1.jpg?dl=0
https://www.dropbox.com/s/31ne2ry2wm..._aft2.jpg?dl=0
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Old 07-05-2018, 10:59 PM   #1882
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Originally Posted by DaveS View Post
 Thanks for finding that schematic GLS. I'm currently in process of redoing the SRB meshes and I needed to be sure of the locations of the holddown posts. This is what I got so far: https://www.dropbox.com/s/j8rh2zpdsu..._aft1.jpg?dl=0
https://www.dropbox.com/s/31ne2ry2wm..._aft2.jpg?dl=0
What about the OV?
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Old 07-05-2018, 11:24 PM   #1883
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Quote:
Originally Posted by GLS View Post
 What about the OV?
Still trying figure a few things out, namely where a weird vertical offset between the TSM carrier plates and the T0 umbilical panels on the orbiter comes from. There seems to be a 10 cm offset between the orbiter and the TSM carrier plates. I've checked everything and everything seems to be in order.
This screenshot illustrates the issue: https://www.dropbox.com/s/nlho4taj8c...Issue.jpg?dl=0
The white box is where the aft ball fittings on the ET should be as measured from the MLP zero level. But as you can see, they're higher than that.

According to my research the MLP zero level is located XO1744 with the ball fittings on the ET are located at XO1317. So with those numbers I created a 10.8458 m tall box with the bottom on the zero level of the MLP. And found out why the TSMs and the orbiter would align properly which something that had been troubling me for a long time.
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Old 07-09-2018, 10:11 PM   #1884
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... and now is the time for someone to point out something that I missed after looking at this for the last week...

So, we need the A/L trajectory parameters for all 4 trajectory variants, and as I don't have them, I have to calculate them. Should be simple enough: 2 lines, 1 circle and 1 exponential.... famous last words...
I got this diagram (don't know from where exactly) from the early days, that shows the trajectory and even has some numbers... that also don't match (keep reading).


The issue is that when using the flare circle parameters (R=28802, X_K=-3060 and H_K=-28932), the exit of the flare circle is not X=-4722;H=178, but X=-3814;H=140.
Trying to calculate the R, X_K and H_K from the tangent points of the 2 glide slopes doesn't work (I'm pretty sure no circle can be tangent to both points at the same time).
The reference equations for the circle part have the vehicle follow the circle, so that part is a "simple" circle, and the same goes for the exponential part afterwards, so the trajectory should all fit, but it doesn't!
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Old 07-11-2018, 10:10 PM   #1885
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In case anyone is interested, I think I finally figured it out: the pull up circle isn't exited at gamma -1.5, but at a gamma that matches the gamma of the exponential. In the diagram above that works out to be -3.308053.
Now I just need to work out new equations to put in the spreadsheet, so I get the needed numbers.

BTW: I never "liked" that indication in the diagram, and the texts, that the vehicle had to increase the descent rate in the exponential part... Now I know it doesn't.
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Old 07-12-2018, 04:28 PM   #1886
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I don't think the short dashed line with an angle of 1.5 degrees in the diagram is a vertical line (which it would appear to be on first glance). I think it is the angle to the intersection point of the Exponential Flare and the Shallow Glideslope.

The angle to a vertical line as you pointed out is ~3.3 degrees.

The height and distance of the intersection of the Exponential Flare and Shallow Glideslope (assuming the 1.5 degrees from above) is H = 130 ft & x = -3969
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Old 07-14-2018, 11:48 PM   #1887
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Bad news: I can't solve this analytically.... I don't know where to "lock" the exponential part in the shallow glide slope, so there are more variables than equations = kaput.

Good news: I just solved this interactively iteratively!
Basically I created a matlab script to run a range of R (radius of the circle), and for each of them the X_EXP (start of exponential) was moved about so the HDOT difference between the circle part and the exponential part decreased (both the H and HDOT must match). I picked the smaller R, which gives the most time in the shallow glide slope, but also give the highest Gs during the pull up.
Compared with the diagram above, the difference isn't that big (I'm sure there is some rounding in it), and the circle and the exponential match with sub-millimeter precision:
X_EXP: -4741.81
H_DECAY: 29.7
R: 28799.6
H_K: 28930.56
X_K: -3060.93


Now, apparently there is a 5s minimum time requirement in the shallow glide slope, which is refined as pitch rate < 0.5/s. There is also a parameter (sigma) that controls the rate of decay of the exponential, thus how fast you converge to the shallow glide slope. These things are of interest because (at least) with the 20 steep glide slope and 6500ft aim point, we totally mess up the shallow glide slope and land WAY too fast. Most of the blame is on the FCS, as we end up ~50ft lower at the end of the flare (which is about 1/3 of the current altitude), but I think that sigma needs some adjustment (at least in this case), so we converge faster to the shallow glide slope and hopefully correct (part of) the altitude error.


EDIT: I just noticed I wrote interactively instead of iteratively Too much work, too little sleep.

Last edited by GLS; 07-15-2018 at 12:01 PM.
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Old 07-15-2018, 09:40 PM   #1888
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Think about sheep !!
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Old 07-16-2018, 09:39 AM   #1889
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Better pay attention or you might end up like me: Spending too much time in the proximity of doctors. I don't recommend it.
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Old 07-16-2018, 06:34 PM   #1890
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I'm sleeping... it just happens to be more like 7h instead of 8. After a while it stacks up and I need to sleep more.... and I didn't.

Anyway, I've been reading the HAL/S manual, and COMPOOL variables (maybe "COMPOOL structures" is a better description) are pretty much like a global variable. I still have to think about it some more, but it's good to know that each variable there "has an owner", which makes it easier for us to load/save from the scenario. We just have to make sure the owner is running or nothing is saved.
I also found out that HAL/S uses 1-based indexes, so now it makes sense why some variables were 1 or 2.

---------- Post added at 07:34 PM ---------- Previous post was at 01:56 PM ----------

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 but it's good to know that each variable there "has an owner", which makes it easier for us to load/save from the scenario.
Not so...
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